Carbon dioxide storage risk assessment: Analysis of caprock fracture network connectivity

A geomechanical risk assessment methodology for CO2 storage has been developed which analyses the connectivity of networks created by fractures in the caprock prior to and post injection. Emphasis is placed on assimilating into the results the uncertainty in the fracture properties at a particular site. The methodology utilises percolation theory and involves modelling large numbers of realisations of the possible distribution of fractures in the caprock and testing whether these realisations contain a network of connected fractures spanning the model region. In addition, shear and tensile failure criteria are applied probabilistically so as to honour the uncertainties present in measurements and models. The results of failure analysis are then used to investigate changes in the caprock fracture network connectivity post injection. The procedures of modifying fracture properties according to a failure analysis and modelling the connectivity of fracture networks are demonstrated with an example study and compared to a deterministic formulation.